1. Field of the Invention
The present invention relates to supervisory control of an optical amplifier repeater system, and particularly to a supervisory system and supervisory method of an optical amplifier repeater system used for long distance optical communications through a submarine cable laid on an ocean floor and the like.
2. Description of Related Art
FIGS. 8-11 are block diagrams showing a conventional supervisory system of the optical amplifier repeater system: FIG. 9 is a block diagram showing the optical transmitter as shown in FIG. 8; FIG. 10 is a block diagram showing an optical amplifier repeater as shown in FIG. 8; and FIG. 11 is a block diagram showing the optical receiver as shown in FIG. 8. In FIG. 8, each reference numeral 101 designates an optical amplifier repeater, the reference numeral 102 designates an optical transmitter, 103 designates an optical receiver and 104 designates a transmission fiber. The optical amplifier repeater 101, receiving an optical signal from the optical transmitter 102 through the transmission fiber 104, amplifies the optical signal, and supplies it to the transmission fiber 104 on the side of the optical receiver 103.
Next, the operation of the supervisory system of the optical amplifier repeater system as shown in FIG. 8 will be described. First, the operation of the optical transmitter 102 will be described with reference to FIG. 9. A main signal circuit 105 outputs a main signal bearing transmitted information, and an auxiliary signal circuit 106 outputs an auxiliary signal with a lower rate and smaller amplitude than the main signal. The two signals are superimposed so that a modulator 107 modulates the multiplexed signal. A driver 108 drives a semiconductor laser 109 in response to the modulated signal to generate the optical signal. The optical signal is transferred to the transmission fiber 104 (shown in FIG. 8) via an internal transmission fiber 110.
Here, the optical signal output from the semiconductor laser 109 includes a main optical signal and an auxiliary optical signal generated by the electric-optic conversion of the main signal and auxiliary signal, respectively. Thus, the optical signal has such a waveform as modulated by the main signal, on which the low rate auxiliary signal of a small modulation factor is superimposed.
The auxiliary signal from the auxiliary signal circuit 106 consists of an operation command for the individual sections or circuits constituting each optical amplifier repeater 101 to inform about their states for monitoring them. The auxiliary signal includes one of proper address codes uniquely assigned to individual optical amplifier repeaters 101 in advance to specify the optical amplifier repeater 101 to be activated.
When the optical transmitter 102 activates a particular optical amplifier repeater 101 by providing the auxiliary signal with one of the address codes proper to the optical amplifier repeater 101, it must consider a time period the optical amplifier repeater 101 will take to execute the command and to make a response, and transmits the subsequent operation commands to other optical amplifier repeaters 101 at suitable intervals to avoid overlapping of the response optical signals from a plurality of optical amplifier repeaters 101.
Next, the operation of the optical amplifier repeater 101 will be described with reference to FIG. 10. The optical amplifier repeater 101 receives the optical signal via the transmission fiber 104 of FIG. 8. A coupler 112 connected to an internal input fiber 111 splits the optical signal, and provides only a small part of the optical signal to a photoelectric converter 121. Most of the optical signal is supplied to an erbium doped fiber amplifier 113.
The optical signal entering the erbium doped fiber amplifier 113 passes through an optical isolator 114, is coupled by a coupling filter 115 with pumping light fed from a pumping laser diode 116, amplified by an erbium doped fiber 117, and passes through an optical isolator 118. A coupler 119 splits the optical signal to extract only a small part of the optical signal as feedback control information. Most of the optical signal is transferred to the transmission fiber 104 as shown in FIG. 8 via an output fiber 120.
The photoelectric converter 121 converts the part of the optical signal into an electric signal, and supplies it to an amplifier 122. The amplifier 122 amplifies the electric signal by a prescribed amount, and supplies it to a lowpass filter 123. The lowpass filter 123 detects the auxiliary signal from the electric signal, and supplies it to a call identifying section 124. The call identifying section 124 compares the address code in the auxiliary signal with the address code of the optical amplifier repeater to identify it, and supplies the identification result to an identification controller 125.
Subsequently, when the identification result of the call identifying section 124 indicates the agreement between the address codes, the identification controller 125 carries out the operation command. For example, when the operation command instructs the notification of level states, the identification controller 125 activates an encoder 126 and a modulator 127 to encode supervisory information indicating whether the levels of various portions are higher or lower than initially set values, and to modulate it to be supplied to the pumping laser diode driver 128.
The pumping laser diode driver 128 drives the pumping laser diode 116 in accordance with the modulation signal fed from the modulator 127, and outputs the pumping light which also serves as a response optical signal including the supervisory information. The coupling filter 115 combines the transmitted optical signal with the pumping light to be supplied to the erbium doped fiber 117.
Thus, the erbium doped fiber 117 amplifies the optical signal based on the pumping light bearing the response optical signal. The amplified optical signal is supplied to the transmission fiber 104 through the output fiber 120.
A photoelectric converter 130, receiving part of the optical signal extracted by the coupler 119, converts the optical signal into an electric signal. An amplifier 131 amplifies the electric signal and supplies it to a feedback controller (not shown). A photodetector 129 detects the output of the pumping laser diode 116, and feeds the detected signal back to the pumping laser diode driver 128.
Next, the operation of the optical receiver 103 will be described with reference to FIG. 11. In the optical receiver 103 that receives the optical signal sent from the optical amplifier repeater 101 through the transmission fiber 104 as shown in FIG. 8, a photoelectric converter 133 receives the optical signal through an internal transmission fiber 132, and converts it into an electric signal. Since the optical signal includes the main optical signal and response optical signal corresponding to the main signal and response signal, they are extracted as the main electric signal and response electric signal.
Subsequently, the amplifier 134 amplifies the electric signals by a prescribed amount. The amplified main electric signal is demodulated by a main signal demodulator 135 as the main signal. A low pass filter 136 extracts the response electric signal. An auxiliary signal demodulator 137 demodulates the response electric signal and outputs the supervisory information. The supervisory information is used as supervisory/control information when operating the optical amplifier repeater 101.
As described above, according to the conventional supervisory system of the optical amplifier repeater system, each optical amplifier repeater 101 encodes the states of the various sections and circuits in response to the request for the state notification, and transmits the information about the states to the optical receiver 103. For example, to implement a desired supervisory function such as temperature control, a straightforward measuring and controlling circuit. However, installing such a circuit will increase the scale of the repeater supervisory circuit, presenting a problem of increasing the size of the repeater.
In addition, as for gain variations, temperature compensation and the like due to characteristic changes with time during operation, since their control system constitutes a closed control system in the supervisory circuit in the optical amplifier repeater, a problem arises in that it is unsuitable for a land side supervisory system (not shown) to monitor the operation states and to control the optical amplifier repeater in response to the supervisory information. Accordingly, it is difficult for the optical amplifier repeater to implement high reliability that enables a long term operation, and to stabilize the gain against the changes with time in the characteristics of the components and circuits during the operation.
Furthermore, to notify of the supervisory states quantitatively, an increasing amount of information is required for the optical amplifier repeater, which presents a problem in that the response signal can have an adverse effect on the main signal.
Moreover, considering the operation time of the optical amplifier repeater to execute the operation command and the arrival time of the response optical signal, the optical transmitter must place certain intervals between transmissions of successive operation commands to the optical amplifier repeater to prevent the optical signal traveling through the optical fiber 104 from including many auxiliary optical signals or response optical signals at the same time, which presents a problem of hindering efficient operation.
The present invention is implemented to solve the foregoing problems. It is therefore an object of the present invention to provide a supervisory system and a supervisory method of an optical amplifier repeater system capable of achieving operation supervision considering characteristics of individual supervisory targets in the optical amplifier repeater, thereby improving its reliability. Another object of the present invention is to provide a supervisory system and a supervisory method of the optical amplifier repeater system capable of implementing gain stabilization and temperature compensation against changes with time in the characteristics of the individual supervisory targets, thereby implementing high reliability.
According to a first aspect of the present invention, there is provided a supervisory system of the optical amplifier repeater system in an optical transmission system including two terminal stations and at least one optical amplifier repeater connected between the two terminal stations through an optical fiber, the supervisory system of the optical amplifier repeater system comprising: an optical transmitter installed in at least one of the two terminal stations for transmitting to the optical amplifier repeater an optical signal including an operation command to notify of a state of a predetermined supervisory target; a response signal generator installed in the optical amplifier repeater for receiving the optical signal transmitted from the optical transmitter, and for generating a response optical signal including a response code indicative of the state of the supervisory target; an optical receiver installed in at least one of the two terminal stations for receiving the response optical signal transmitted from the optical amplifier repeater; and an information processing unit connected to the optical receiver for generating a numerical form of the response code included in the response optical signal received by the optical receiver by using a predetermined expression that links the response code with measured information obtained by measuring in advance the supervisory target with an external measuring device during operation of the optical amplifier repeater in response to the operation command.
Here, the information processing unit may comprise a storage for recording the expression in advance; an arithmetic unit for converting the response code into the numerical form using the expression; and an arithmetic result output unit for outputting information about the numerical form output from the arithmetic unit.
The expression can be obtained in terms of variations in the response code in response to variations in the measured information about the supervisory target due to ambient temperature changes of the optical amplifier repeater.
The expression can be obtained in terms of variations in the response code in response to variations in the measured information about the supervisory target due to elapsed time.
The supervisory system may comprise a plurality of optical amplifier repeaters installed between the two terminal stations via the optical fiber, and the expression can be obtained for each of the plurality of optical amplifier repeaters to be stored in the storage of the information processing unit.
According to a second aspect of the present invention, there is provided a supervisory method of an optical amplifier repeater in an optical transmission system including two terminal stations and at least one optical amplifier repeater connected between the two terminal stations through an optical fiber, at least one of the two terminal stations including an optical transmitter and an optical receiver, the supervisory method of an optical amplifier repeater comprising the steps of: transmitting from the optical transmitter to the optical amplifier repeater an operation command to notify of a state of a predetermined supervisory target; storing a predetermined expression linking measured information with a response code in advance, the measured information being obtained by measuring the predetermined supervisory target by an external measuring device while the optical amplifier repeater is operating in response to the operation command, and the response code being output from the optical amplifier repeater in response to the operation command; and converting the response code which is sent from the optical amplifier repeater to the optical receiver in response to the operation command, into a numerical form by using the predetermined expression.
Here, the expression can be obtained in terms of variations in the response code in response to variations in the measured information about the supervisory target due to ambient temperature changes of the optical amplifier repeater.
The expression can be obtained in terms of variations in the response code in response to variations in the measured information about the supervisory target due to elapsed time.